An attempt has been made to consider all features of seal ring design including configuration@ materials@ hardness@ dimensions@ surface finishes@ surface treatment@ leak testing@ and general quality. In addition to this@ allowable cylinder breathing and general quality requirements of mating hardware are discussed. Also@ at the end of this report@ there is a brief paragraph on other types of seal rings. PURPOSE This report is intended for use by those people involved in the design and application of high temperature hydraulic systems and components. It is@ in essence@ a first attempt at the standardization of seal ring@ groove@ and gland design for hydraulic piston heads. Specifically@ the report covers some design@ application@ and test aspects of metallic seal rings for reciprocating hydraulic service at -65 F to +630 F fluid or ambient temperature and up to 4000 psi for cylinder diameters ranging from 1/2 inch to 6 inches.